One proposed structure of the power output apparatus includes an internal combustion engine, two motors, a Ravigneaux planetary gear mechanism, and a parallel shaft-type transmission arranged to selectively link two output elements of the planetary gear mechanism to an output shaft (see, for example, Patent Document 1). The power output apparatus of this proposed structure is applicable to the front wheel-drive vehicle. In the power output apparatus of this structure, the internal combustion engine is horizontally arranged, and the internal combustion engine, the planetary gear mechanism, the two motors, and the parallel shaft-type transmission have rotating shafts extended in parallel to one another. Another proposed structure of the power output apparatus has a planetary gear mechanism including an input element connected with an internal combustion engine and two output elements, and a parallel shaft-type transmission including a countershaft connected with the respective output elements of the planetary gear mechanism (see, for example, Patent Document 2). In the power output apparatus of this proposed structure, the two output elements of the planetary gear mechanism are respectively fixed to the inner circumferences of corresponding rotors in an electric driving system. A conventionally known structure of the power output apparatus has a power distribution mechanism including an input element connected with an internal combustion engine, a reactive force element connected with a first motor generator, and an output element connected with a second motor generator, and two clutches arranged to selectively link an axle as an output member with the output element or with the reactive force element of the power distribution mechanism (see, for example, Patent Document 3). In the power output apparatus of this conventional structure, when the first motor generator is rotated at a negative rotation speed to perform power operation, the two clutches are controlled to connect the reactive force element of the power distribution mechanism with the output member and disconnect the output element of the power distribution mechanism from the output member. Such control prevents the occurrence of power circulation where the first motor generator is driven with electric power generated by the second motor generator that uses part of the power of the output member.    Patent Document 1: Japanese Patent Laid-Open No. 2005-155891    Patent Document 2: Japanese Patent Laid-Open No. 2003-106389    Patent Document 3: Japanese Patent Laid-Open No. 2005-125876